OVERVIEW OF HEAT -Specific heat - Latent heat of vaporization - Transmission of heat

HEAT

Heat capacity

Heat is an agent that produces the sensation of warmth. When an object is heated, its molecule begins to move faster. Heat always flows from a hotter body to a colder body.

        The temperature of a substance is the degree of its hotness or coldness. Three temperature scales commonly used to measure temperature are the Celsius scale, the Fahrenheit scale, and the Kelvin scale. The SI unit of temperature is Kelvin (K).

Specific heat

          Specific heat of a substance is the ratio of the heat required to raise 1 gm of it through 1⁰C to the heat required to raise 1 gm of water through 1⁰C.

        The thermal capacity of a body is the quantity of heat regulated to raise the temperature of the body through 1⁰C.

Latent Heat

        When a solid is heated its temperature remains constant. So the heat supplied at the melting point of a solid is used not to raise its temperature but to convert the solid to a liquid state. This heat is called the Latent heat.

        The latent heat of fusion of a solid is the quantity of heat required to convert one gm of the solid at its normal melting point into a liquid without rising temperature. The latent heat of the fusion of ice is the quantity of heat required to convert one gm of ice at 0⁰C into water at 0⁰C.

Latent heat of vaporization

        Latent heat of vaporization of a liquid is the quantity of heat required to convert on gm of the liquid at its boiling point into vapour without rising temperature.

        The latent heat of steam is the quantity of heat given out by one gram of steam at 100⁰C when converted into water at 100⁰C.

Vapor pressure

        The space above a liquid in the enclosure always contains the vapour of the liquid. The pressure exerted by this vapour on the liquid surface is called vapour pressure.

Transmission of heat

Conduction is the process by which heat is transmitted from the hot to the cold end of a body without the actual movement of the particles of the body.

        For instance, when one end of a metal rod is heated, the heat is transmitted through the successive layers to the other end. In this case, heat is communicated through the successive layers of the rod without the movement of the layers.

        The substances which readily transmit heat by conduction through them are called good conductors. Substances that do not readily transmit heat by conduction are called poor conductors. Usually, metals are good conductors like copper and aluminium but non-metals are poor heat conductors like glass and wood.

Convention

Convention is the process by which heat is transmitted through a medium by the actual movement of the heated particles of the medium. Convection takes place only in liquids and gases.

        For instance, if water in a beaker is heated, the bottom layer receives heat, becomes less dense, and rises. The colder, denser water at the top sinks down. This in turn gets heated and rises up. Thus the whole water gets heated. This process of transmission of heat is called convection.

Radiation

        Radiation is the process by which heat is transmitted from one place to another without the help of any material medium.

        For instance, the sun’s heat reaches the earth after travelling empty space and then the atmosphere. The atmosphere is not heated due to the radiant heat passing through it. This process of transmission of heat is called radiation.